Percussion multi-blow gravity drill



NOV 5, 1968 A. E. BARDWELL PERCUSSION MULTIBLOW GRAVITY DRILL Filed July2e, 196e United States Patent 3,409,091 PERCUSSION MULTI-BLOW GRAVITYDRILL Allen E. Bardwell, Princeton, NJ., assgnor to Trident Industries,Inc., Princeton, NJ., a corporation of Delaware Filed July 26, 1966,Ser. No. 567,927 Claims. (Cl. 173--119) ABSTRACT OF THE DISCLOSURE Anovel gravity drop multiblow percussion drill comprising an elongatedcasing closed at the upper end by a plug adapted to be attached to acable connector and at the lower end by a stationary `anvil adapted t0receive a drill bit at its free lower end, an elongated heavy hammerreciprocably mounted in the casing having reduced extremities about eachof which is mounted a heavy compression spring which in rest uprightposition of said drill maintain said lower end of the hammer spaced apredetermined short distance from the anvil, said springs beingyieldable to permit initial and subsequent striking of the anvil by thehammer immediately following striking of a drill bit mounted in theanvil.

The present invention relates generally to gravity drop -percussiondrills, and more particularly to a novel percussion gravity drop drillincorporating structure for effecting one or more blows immediatelyfollowing the gravity drop blow of the bit.

Efforts have long been made to improve gravity drop or churn drilling inthe area of multiple vblow structure. It has been recognized for yearsthat the number of feet drilled per hour in Irock, or the like, can bematerially increased by striking one or more additional blows throughthe bit immediately following the gravity blow thereof. Structuresheretofore devised by others have had little, if any, practical success.

Hence, an object of the present invention is to provide a novelpercussion multi-blow gravity drop drill comprising one solution to thelong existing problem.

In brief, the present novel drill includes in a preferred embodiment anelongated casing having an upper plug for attachment to a cableconnector and a fixed anvil assembly secured in the lower end thereofcomprising an anvil portion and a shank portion having a threaded socketfor receiving a drill bit. Within the casing is a reciprocatable hammerhaving reduced upper and lower extensions, there being a compressionspring about each extension. In the normal position of the hammer, withrespect to the casing, there is a short gap between the face of thelower extension and the anvil. When the drill descends and strikes thehole bottom the internal hammer continues its descent, closing the shortgap and compressing the lower spring to deliver a follow-up blow to theanvil and hence to the drill bit. The hammer may then rebound,compressing the upper spring, `and a series of follow-up blows mayresult. Upon retraction of the drill up the hole, the two compressionsprings will return the hammer to the normal position, of a short gapIbetween hammer and anvil prior to the succeeding dropping of the drilland striking of the hole bottom.

Therefore, other objects of the invention are to provide a novelpercussion multi-blow gravity drop drill which is of durable, ruggedconstruction insuring good commercial use of the tool, whichincorporates effective multi blow structure that materially increasesthe per hour drill footage, which is adapted to a variety of drillinguses, and which otherwise fulfills the objects and advantages soughttherefor.

The foregoing and other objects and advantages are 3,409,091 PatentedNov. 5, 1968 apparent from the following description taken with theaccompanying drawings, in which:

FIGURE 1 is longitudinal cross-sectional view of the upper portion of agravity drop drill incorporating the teachings of the present invention,portions of the upper plug and of the middle portion of the hammer andcasing Ibeing broken away for conservation of space and the upperportion of the plug being 'shown in elevation; and

FIGURE 2 is a longitudinal cross-sectional view through the lowerportion of the drill of FIGURE 1, portions of the lower shank portionbeing omitted for conservation of space and the lower shank portionbeing shown in elevation.

Referring to the drawings more particularly by reference numerals, 10indicates generally a gravity drop drill constructed in accordance withthe principles of the pre'sent invention. The drill 10 includes anelongated cylindrical tubular casing 12, which may be integral, asshown, and may be any desired length, as some fourteen feet long in anexperimental tool. An upper plug 14 of the configuration clearly shownin the drawings is screwed into the upper end of the casing 12, suicientlength of threads being provided to effect the total desired compressionin two springs, identified below, in the process of screwing the plug 14to its installed position.

Reciprocally mounted within the casing 12 is a massive hammer unit 16including a central principal hammer body portion 18, an upper reducedshaft portion 20, and a lower reduced 'shaft portion 22. The free lowerend part of the lower reduced shaft portion 22 may be of tough, hardenedsteel. The upper reduced shaft portion 20 reciprocates in an upperbearing 24 which supports and guides the upper end of the massive hammerunit 16 in its reciprocation in the casing 12. This upper bearing 24 maybe made from a nylon tubing, or other suitable long lasting material.Surrounding the upper hammer shaft portion 20 below the bearing 24 is aheavy compression spring 26 which engages a bearing protection shim 28at its upper end. Surrounding the lower hammer shaft portion 22 is asecond heavy compression spring 30 similar to the spring 26 whichengages at its lower end a bearing protection shim 32 abutting a lowerbearing 34 within which the lower reduced shaft portion 22 reciprocatesas a guide and support. Below the lower bearing 34 is a lower bearingsupport shim 36 having a larger inside diameter 38 at the bottom toprovide a debris chamber 40 around a raised anvil surface, identifiedbelow. The debris chamber 40 is designed and provided to capture anyparticles of metal, nylon, or the like, which may fall from variousinternal components of the drill 10 during its functional life.

An anvil assembly 42 is secured in the lower end of the casing assembly12 by sweating, by threads, or otherwise, and includes an anvil cap 44which receives the chatter of impacts from the hammer unit 16, and alower shank portion 46 including a threaded bit socket 48 whichremovably receives a bit of selected design.

Inasmuch as in the operation of the drill :10, a bit mounted in thesocket 48 of the anvil unit 42 can remain in contact with the surface tobe drilled for only a very small fraction of a second during each cycle,precise synchronization and positioning of the hammer unit 16 arecritical. For proper operation, the opposing springs 26 and 30 should bemaintained under several hundred pounds of compression and theequilibrium position of the hammer unit 16 in free fall should be suchas to provide a small fraction of an inch gap between the lowerextremity of the hammer unit 16 and the anvil cap 44. That is, thesprings 26 and 30 should counterbalance in a position such that the gapbetween the lower extremity of the hammer unit 16 andthe anvil cap 44 isless than one-half Y L3 inch. If this gap is made much larger thanone-half inch, except in soft material, the probability of the hammerunit 16 delivering its impact to the anvil cap 44 during the shortperiod of time when said anvil assembly 42 is still in contact with thebottom of the bore is greatly reduced and the eiciency of drillingsuffers. Successful experimental models of this drill 10 have lbeenconstructed where this gap is one-quarter inch, The .extent of the gapwill lvary, however, in practice depending upon the nature of the groundor rock in which drilling is taking place.

In the operation of the drill, the upper and lower compression springs264 and 30 are both under compression when the drill is descending tohold the hammer unit 16 raised above the anvil cap 44 to form the shortgap described above. Then, when the drill strikes the hole bottom, sothat the downward stroke of the casing 12 is arrested, the hammer unit16 will continue to descend and further compress the lower spring 30.The hammer closes the short gap and strikes the anvil assembly 42afollowupblow that is delivered through the drill bit to the hole bottomfor additional drilling impact. The' gap length,` mass of hammer andspring forces are selected to have the follow-up below occur while thedrill bit is contacting the hole bottom, thereby increasing drillingeciency.

The hammer unit 16 will rebound from the anvil assembly 42, and theupper spring 30 functions to absorb and redirect rebound forces, suchthat a series of followup blows may occur. The upper spring 30 must alsobe under such compression and have such a spring constant during descentof the drill as to act as an abutment, or

stop, that resists the upward force of the lower spring 26 to establishthe short gap between the lower end of the hammer unit 16 and the anvilcap 42. The lower spring 26 must exert an upward force adequate tosupport the mass of the hammer unit 16 and to work against the upperspring 30 in establishing the short gap. Adjustment of the springcompression can be made by altering the length' of the bearingprotection shims 28, 36, and by selection of the springs 26, 30.

It is clear that this design depends primarily on the inertialfollow-through action of the hammer unit 16 subsequent to the initialimpact of the anvil assembly 42 with the bottom of the bore and theredirection of the resulting rebound forces to energize its hammer unit16 to produce a chatter of impacts upon said anvil cap 44. This designoffers a substantial increase in eiciency over stanlard churn drills.

It is apparent that there has been provided a drill construction whichfulfills the objects and advantages sought therefor,

It is to be understood that the foregoing description and theaccompanying drawings have been given by way of illustration andexample. It is also t-o be understood that changes in form of theelements, rearrangement of parts, and substitution of equivalentelements, which will be obvious to those skilled in the art, arecontemplated as within the scope of the present invention, which islimited only by the claims which follow.

What is claimed isc l 1.` A multi-blow gravity drop drill structurecomprising an elongated casing, means closing the upper end of-thecasing including means for attachment to a raising and droppingstructure, an anvil member secured to and closing the lower end of-saidcasing, said anvil member including means for detachably receivingabitya-single hammer member reciprocably mounted in said casing adaptedto strike said anvil member immediately following the impact of thedrill structure through an attached bit with the bottom of a hole, afirst compression spring acting downwardly upon said hammer member, anda -second compression spring acting upwardly upon said hammer mem-ber,said springs in a dropping drilling position of said drill beingsubstantially in equilibrium and maintaining said hammer member spaced asmall distance from said anvil member.

2. The combination of claim 11 in which said springs remain undercompression.

3. The combination of claim 1 in which said dropping drilling positionsaid springs maintain said spacing between anvil member and hammermember at less than one-half inch.

4. The combination of claim 1 in which the spacing between the hammerand the anvil members at the moment of contact of the drill at thebottom of a hole in hard rock and the like is less than about one-halfinch.

5. The combination of claim 1 in which the spacing between the hammerand the anvil members at the moment of contact of the drill at thebottom of a hole in soft material is greater than one-half inch.

References Cited UNITED STATES PATENTS 1,835,189 12/1931 Spencer 175-299X 2,524,707 10/1950 Koeln 175-299 2,655,825 10/1953 Gendron 173-121 X2,765,776 10/1956 Pyk 173-118 X 2,835,474 5/1958 OConnor et al 175--2992,872,158 2/1959 Green 175-299 3,151,912 10/1964 Herrmann 173-121 X3,303,899 2/1967 Jones et al. 175-299 3,305,034 2/1967 Koeln 175-2993,307,641 3/1967 Wiggins 175+-56 CHARLES E. OCONNELL, Primary Examiner'.

I. A. CALVERT, A ssistanl Examiner.

